Chapter 14 Network Security

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20 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

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Module 12

Network Security


Developing a Network Security Policy


Threats to Network Security


Implementing Security Measures


Appling Patches and Upgrades



Developing a Network Security Policy

Accessing Security Needs

There must always be a delicate
balance between security and

The more accessible a network is,
the less secure it is.

When it comes to a computer
network, how much security is

There are several factors to

The type of business in which
the company engages

The type of data stored on the

The management philosophy
of the organization

Acceptable Use Policy

The first step in creating a security policy for a
company network is to define an Acceptable Use
Policy (AUP).

An AUP tells the users what is acceptable and
allowed on the company network.

To view some examples of AUPs, visit these

Username and Password Standards

Usually the system administrator will define the naming convention for
the usernames on a network.

A common example is the first initial of the person's first name and
then the entire last name.

A complex username naming convention is not as important as
having a complex password standard.

When assigning passwords, the level of password control should
match the level of protection required

Rules for Network Access

A system administrator who assigns the proper
permissions on the share drives and directories
defines the rules for network access.

By assigning the proper security permissions on the
network, the system administrator should know who
has access to specific directories.

Proper maintenance by the system administrator will
be required to examine auditing logs of attempts that
have been made to access the network shares.

Policy for Disposal of Materials

Hardware, software, and data should never just be
thrown away.

There are strict regulations that should be followed to
control the disposal of computer components.

The system administrator is responsible for
developing a policy based on environmental and
safety guidelines for hardware that no longer works.

To view some examples of the disposal of materials
policies visit these websites:

Virus Protection Standards

Place proper filters and access lists on all the
incoming gateways to protect the network from
unwanted access.

To prevent viruses, e
mail policies also need to be
developed that state what may be sent and received.

These websites provide sample e
mail policy

Online Security Resources

based resources offer critical information and
powerful tools that can be used to protect a network.
Some of the best online security resources are the NOS
manufacturer websites

To view examples of the online

security resources visit these


Server Room Security

To protect computing
resources, make sure that
there is a locked door and
four walls between the
server and the rest of the

There are a variety of ways
to permit or deny access to
that area after it has been

The lock and key is a tried
and true method for
physically securing the
server environment.

This method works great if
there are a limited number of
people who need access.

Server Room Security

Using a combination locking mechanism is similar to a lock and
key. The advantages to this method:

Keys no longer have to be distributed

Key control lists no longer have to be maintained

Combinations can also be reset when needed

The one drawback to this model is that it is very easy to share a
combination with someone not authorized.

Card readers are the most common of the access control

They work by reading a magnetic signature off an access card or

A biometrics based access control system uses measurable
physical characteristics to authenticate users into an environment
(fingerprints, retinal patterns, or speech).

Theft Devices

for Server Hardware

A common security measures is the locking mechanism
included as part of the server itself.

Most high end servers enable the case to be locked, and in
many cases to lock the drives into the server chassis.

Almost all rack systems include locking front and back doors.

Removable media drive locks

are locking devices

These devices fit over the floppy drive, zip drive, and CD
ROM drive to prevent unauthorized access.

Some servers are shipped with holes in the cases, which are
predrilled for a padlock.

Alarms are the final add
on, and best suited for the shared
office environment.

Securing Removable Media

Security of removable media includes the following:

Removable disks, floppy, Zip, Jaz, LS120, CD

Removable hard drives

Backup media, tapes

Several methods are used to ensure the security of
removable media:

Lock the media in an office

Place the media in a locked cabinet with strict key control

Place the media in a safe, or a fire
resistant safe

Engage a third
party firm to store the tapes in their secure

Threats to Network Security

Overview: Internal/External Security

The Internet essentially
works by following rules
that are open to the public.

If one studies the rules
enough, one is bound to
find loopholes and
weaknesses that can be

The number of individuals,
organizations, and
institutions connected to
the Internet are growing.

Connecting to the Internet
opens the door to network

Outside Threats

Several outside sources can cause attacks


the true hacker desires to dissect systems
and programs to see how they work.


those that break in to computer systems to
tamper with, steal, or destroy data.


it causes some unexpected and usually
undesirable event.


a self
replicating virus that does not alter files
but resides in active memory and duplicates itself.

Trojan horse

is a program that presents itself as
another program to obtain information

Denial of Service (DoS)

A DoS attack occurs when the targeted system cannot
service legitimate network requests effectively.

As a result, the system has become overloaded by
illegitimate messages.

DoS attacks originate from one host or a group of

When the attack comes from a coordinated group of
hosts, such attacks are called Distributed DoS

A common DoS attack is to overload a target system
by sending more data than it can handle.

Denial of Service (DoS)

There are several specific
types of DoS attacks:

A buffer overflow attack is
designed to overwhelm the
software running on the
target system.

The so
called ping of death
is a well known buffer
overflow DoS attack.

The TCP synchronization
(SYN) attack exploits the
TCP protocol three

The attacker sends a large
volume of TCP
synchronization requests
(SYN requests).

Distributed Denial of Service (DDoS)

Before the hacker can attack the
ultimate target, a "fleet" of
"zombies" (unsecure host with a
permanent Internet connection)
must be coordinated for the

The hacker takes advantage of
the zombie's lack of security.

The hacker breaks in to the
system either directly or through
an e
mail virus.

The goal of the break in or virus
is to install software on the
zombie system.

The hacker uses the zombies to
launch a DDoS attack on the
ultimate target.

Well Known Exploits

Each combination of NOS and
application software contains it’s
own unique set of vulnerabilities
and weaknesses.

Threats to network security
comes from individuals with
sophisticated tools.

Some of these individuals are
often called "script kiddies".

Script kiddy is a negative term
used to describe immature
individuals that use scripts,
software programs, or
techniques created by other,
more skilled crackers.

Trojan Horse Programs

A Trojan horse is a program that presents
itself as another program to obtain information.
For example, there is a Trojan horse that
emulates the system login screen.

When users type in their account name and
password, the information is stored or
transmitted to the originator of the Trojan

The username and password can then
be used to gain access to the system.

Inside Threats

Corporate espionage is the most
sophisticated type of internal
security threat.

Employees can be approached
by competing companies.

There are freelance corporate
spies who take assignments on a
contract basis.

Internal security breaches can
also be the result of rebellious
users who disagree with security

While not accidental, these
breaches are not designed to
cause harm.

Implementing Security Measures

File Encryption

File encryption is a way of
encrypting data stored on a
computer disk so that it is
unreadable to anyone but the
creator of the data.

Windows 2000 includes a file
encryption function.

Windows 9x and Windows NT
do not.

Third party encryption programs
are available for OSs

PC Guardian, Deltacrypt,

IP Security

IPSec secures data at the
packet level.

It works at the network layer of
the OSI model.

The Authentication Header
(AH) enables verification of
the sender identity.

Encapsulating Security
Payload (ESP) ensures the
confidentiality of the data

IPSec can operate in either
the transport mode or the
tunnel mode.

Secure Sockets Layer (SSL)

SSL was developed by
Netscape to provide
security for its web

It uses public and
private key encryption

SSL operates at the
application layer and
must be supported by
the user application.

mail Security

mail users think they have
the same expectation of
privacy when sending e
as they do when sending a
letter through the postal

A more accurate expectation
would be to assume that the e
mail is like a postcard that can
be read by anyone who
handles it during its journey
from sender to recipient.

They often travel through
dozens of nodes or servers on
their way from sender to

Public/Private Key Encryption

One key is published and is widely available.

The other key is private and known only to the user.

Both keys are required to complete the secure

This type of encryption, is also referred to as
asymmetric encryption.

With this type of encryption, each user has both a
public and a private key, called a key pair.

Appling Patches and Upgrades

Finding Patches and Upgrades

Patches are fixes to existing software code.

A NOS manufacturer typically provides security

Microsoft now includes the option to use software called
Windows Update with its operating systems.

Selecting Patches and Upgrades

Software makers recommend installing software security
patches immediately.

This is done to reduce exposure to known vulnerabilities.

Software venders release security updates as soon as they
are available.

Understanding the effect on the system will help determine
if an update, fix, or patch is necessary.

Applying Patches and Upgrades

Periodically, NOS vendors issue updates to their network
operating systems. These updates have various names:

Microsoft Service Packs

IBM Fixpacs

Novell Patches

These updates usually fix bugs or close security holes that
have been found in the released version of the OS.

Download the updates from the network operating system
vendor’s website.


Introduction to Firewalls and Proxies

A proxy is software that
interacts with outside
networks on behalf of a
client host.

Typically, client hosts on a
secure LAN request a web
page from a server running
proxy services.

The proxy server then goes
out on the Internet to
retrieve the web page.

The web page is then copied
to the proxy server, this is
referred to as caching.

Introduction to Firewalls and Proxies

Administrators use Network

Address Translation (NAT) to
alter the source address of
packets originating from a
secure LAN.

This allows secure LANs to be
addressed using private IP

Private IP addresses are not
routed on the Internet.

An outside hacker cannot
directly reach a computer with a
private address.

Some experts make a
distinction between NAT and a
firewall. Others look at NAT as
part of a comprehensive firewall

Packet Filtering

The most basic firewall
solution is an IP packet filter.

To configure a packet filter, a
network administrator must
define the rules that describe
how to handle specified

The most basic firewall
solution is an IP packet filter.

To configure a packet filter, a
network administrator must
define the rules that describe
how to handle specified

Packet Filtering

Both TCP and UDP use port numbers to address specific
applications running on a host.

Both TCP and UDP use port numbers to address specific
applications running on a host.

Firewall software must guess at what connectionless traffic
is invited and what connectionless traffic is not.

The most comprehensive form of packet filtering examines
layer 3 and 4 headers and the layer 7 application data as

Layer 7 firewalls look for patterns in the payload of the

This is done in an effort to determine what application is
being used, such as HTTP, FTP, and so on.

Firewall Placement

A boundary router connects
the enterprise LAN to its
ISP or the Internet.

The boundary router should
only allow HTTP, FTP, mail,
and DNS related traffic to
the DMZ.

The DMZ is designed to
keep the inside network

The NOS servers in the
DMZ should be tightly

Common Firewall Solutions

The PIX Firewall 515 uses TFTP
for image download and upgrade.

It has a low profile design, 128,000
simultaneous sessions, and 170
Mbps thru

The PIX Firewall 520 uses a 3.5
inch floppy disk drive to load the
image and upgrade.

It has an enterprise chassis
design, 256,000 simultaneous
sessions, and 240 Mbps thru

The PIX Firewall is secure right out
of the box.

Default settings allow all
connections from the inside
interface access to the outside

Common Firewall Solutions

The Cisco IOS Firewall
Feature Set provides
stateful packet filtering.

Another firewall solution is
a UNIX host.

The UNIX host serves as
a router, running packet
filtering software such as
ipfw, and/or NAT.

Home users have a
variety of firewall options
available as well.

Using an NOS as a Firewall

In high
traffic environments, a specialized packet
filtering and NAT solution is recommended.

A device such as a router or firewall appliance is
designed to switch packets and manipulate them

A NOS running on ordinary hardware may be able to
do the job.

However, it is not without adding latency and overhead
on the server.

In low traffic environments, such as small offices and
home networks, a NOS firewall solution is a good